1. Field of the Invention
The present invention generally relates to a method of post-tensioning a truss of substantially conventional steel construction provided with concrete encasement or cladding of certain chords while the truss is in a fabrication yard or at ground level before erection and installation. Specifically, the invention relates to a method of making the truss as described above in which the structural steel truss is first assembled in a fabrication yard with certain of the chord being provided with formwork. Reinforcing steel and steel tendons are placed in the formwork and concrete is poured to encase the chords of the truss, the reinforcing steel and steel tendons while the truss is positioned horizontally or vertically in the fabrication yard or at ground level. The steel tendons are then partially or fully post-tensioned to provide maximum load support capability. The cladded and partially or fully post-tensioned truss are then lifted to an installation point and a load deck placed on the truss with final post tensioning of the truss then being completed. The truss of the present invention can be used in situations where trusses are used to carry heavy loads over long spans such as bridges, stadiums, convention halls and the like and is especially beneficial when spanning a busy highway or waterway since the trusses are assembled, cladded with concrete and partially post-tensioned before being lifted and placed in an installation site.
2. Description of the Prior Art
Various types of trusses are well known with the trusses being supported in various manners to produce tension or compression forces in the components of the truss. It is also well known to encase or clad certain of the components of the truss in concrete for increasing the strength, insulation and fireproofing of the truss. In my above-mentioned copending application, a truss is erected at the installation site and formwork is associated with the components of the truss to be encased in concrete with the concrete cladding having reinforcements and steel tendons for post-tensioning with the cladding and post-tensioning being accomplished after the truss is at the installation site. However, prior truss structures do not include the concept of encasing the top and bottom chords or other components of the truss in concrete in the fabrication yard or at ground level prior to being placed at the installation site and then partially or fully post-tensioning the steel tendons while the truss is either in a vertical or horizontal position. The completed and cladded truss that is partially or fully post-tensioned then is lifted or otherwise placed in an installation site and a load deck or other load is placed thereon with the truss then being final post-tensioned.